Starting with Oracle 12c, Oracle does not require you to set the database in hot-backup mode to create a recoverable crash-consistent snapshot.
To use the Oracle Storage Snapshot Optimization feature, the snapshot of a live database requires that the storage devices underlying the database must be consistent with the same point in time (crash consistent) and that write-order fidelity is maintained. During full database recovery from a crash-consistent snapshot, the Oracle recovery process ensures that the archive logs are applied from a database checkpoint prior to the snapshot up to the latest committed transaction from the Online Redo Logs.
The Storage Snapshot Optimization feature is important because it allows you to take consistent snapshots at short intervals. Each snapshot is a valid database backup that can be used to recover the database if needed.